KABUL, Afghanistan (CNN) -- A misunderstanding between local police and coalition forces led to an airstrike in southwestern Afghanistan on Sunday that left nine police officers dead, a defense ministry official said.

The nine officers were mistaken for Taliban militants by coalition forces, said Gen. Mohammad Zahir Azimi.

The aerial attack took place in the Anar Derah district in Farah province. It was conducted by U.S. soldiers and troops from the Afghan army, Azimi said. He did not have any further information about the attack.

Last week, an airstrike by the U.S-led coalition in the province struck and killed eight civilians. The airstrike was launched after a coalition convoy was attacked.

In an unrelated incident over the weekend, two mortar rounds fired by NATO-led troops killed four civilians and wounded four others in southeastern Afghanistan on Saturday night, the International Security Assistance Force said.